H/L Compression Good or Bad

[TurboNutzz]

From what i've been reading, boost is bad for high compression enigines because its creating too high of a pressure in the cylinders which causes lots of problems. but i also read that its actually not that bad as some say. assuming we strengthen the internal, articles have said "why lower the compression to run more boost. cause boost is upping the compression any way. so way take away whats already there. just run less boost with out altering the high compression" and its not from any advertisement. its on those techy pages.

So what do you guys say about this.....any help would be great thanks....

[turbo2nr]

ok seems to make sence right?

why lower the compression to run more boost. cause boost is upping the compression any way. so way take away whats already there. just run less boost with out altering the high compression"

ok from what i get we lower compression to run more boost.. more boost more hp more hp faster car.. right.. if you dont rasie boost and run low boost you will not make that much hp..

lets say for arument sake we have a honda motor with reinforced internals but sill hi compression and only runs 12psi.. lets say he makes 250hp.. no lets take that same motor and reinforce the internals nad drop compression and raise the boost to 18psi and now that honda is makin 300+hp..

from what you were saying is that turbo raise compression.. and by us droppin compression we takin away what already there.. but if we do lower compress. we can boost more on the motor and make more hp..


im sorrie if i made no sence

1

[civicgsr_T4_60-1]

what he said

[boosted331]

Adding boost makes more power than adding compression, more often than not. You can only compress the air so much (with compression and turbo boost) before there is too much heat in the cylinders and the mixture lights off or detonates. So while a 10:1 motor will give you more low end, and make more power per pound of boost (given equal timing) and spool the turbo sooner than a lower compression motor, you can't run as much boost and won't make as much top end horsepower. If you're building a 1.5-1.7 liter street honda, 9.5:1-10:1 is a good compression ratio range to give you good spool but still let you run some boost on the street (given a good tune, don't try and use a shitty FMU or the AFC hack or an SMC), for a 1.8-2.0 around 9:1 is good because they naturally have more low end because of increased displacement, and for an H22 or anything else over 2 liters anywhere from 8.5:1 to 9:1 is good.

[civicgsr_T4_60-1]

another well put explantion. I think i'll just agree with everyone today.

[spdbtr79460]

Theres gonna be trade offs on whatever you do. If you lower the compression too much it will not give you the low end needed for everyday driving. Plus it gives you a bigger margin for error on a lower compression motor. If you keep a higher compression it will give you the low end but you hav a smaller margin for error but have it tuned really good. Just depend on what you want for your motor. N E ways good luck

[PWMAN]

The simple quick answer-
Lower compression with more boost makes more power than high compression low boost.

[TurboNutzz]

thanks for the info, i was wondering about the trade off, but it seems boost with low is the preffered method......ill probably go with the 9.0.1 pistons.....thanks again.........

[super_man_3179]

I like the idea of a little higher compression and lower boost. It will give you more low end and spools the turbo REALLY fast. That way you don't have to boost the hell out your engine. If your a daily driver 9.5-10 should be a decent compression ratio The RSX has 11:1 compression ratio...LOOK what happens when you turbo that!!!! Too low of a compression ration will not give you the low end you need for daily driving. Daily driving will be a high RPM fiasco!! 5000RPMS everywhere so you have enough torque to get up that hill...and massive turbo lag...But top end will RULE over a high comp. low boost. If you are planning on drag racing...low comp. high boost.....Daily driving...Stock or a little higher comp...and lower boost......

Remember each pound of boost doesn't give you the same power on every car.

[PWMAN]

Originally Posted by super_man_3179

I like the idea of a little higher compression and lower boost. It will give you more low end and spools the turbo REALLY fast. That way you don't have to boost the hell out your engine. If your a daily driver 9.5-10 should be a decent compression ratio The RSX has 11:1 compression ratio...LOOK what happens when you turbo that!!!! Too low of a compression ration will not give you the low end you need for daily driving. Daily driving will be a high RPM fiasco!! 5000RPMS everywhere so you have enough torque to get up that hill...and massive turbo lag...But top end will RULE over a high comp. low boost. If you are planning on drag racing...low comp. high boost.....Daily driving...Stock or a little higher comp...and lower boost......

Remember each pound of boost doesn't give you the same power on every car.

Good luck trying to boost the RXS-S more than 3-4 PSI on pump gas, and that might yield you 40-50 more HP. But lower the compression to 10:1, and run 10 PSI-you will loose maybe 10 HP from the lower compression, but gain about 120 HP. Which sounds better?
Low end is not affected as much as you think just dropping the CR down 1 point. Displacement has WAY more to do with low end power. Thats why the B18B1 is so great to boost, it has a low CR of 9.2:1 and it has a fairly large displacement (for Hondas anyway) and long stroke. You can surpass the B18C1's power output because of the high boost/low compression ratio of the B18B1 also making MORE low end power because of more displacement.